Association of serum vitamin D status with serum pro-inflammatory cytokine levels and clinical severity of fibromyalgia patients

Background & aim: The role of vitamin D deficiency in fibromyalgia (FM) pathogenesis is not clearly understood. In this study, we evaluated the association of serum vitamin D status of FM patients with laboratory indices of inflammation, as well as clinical indices of FM. Materials & methods: Ninety-two female FM patients with a mean age of 42.4 ± 7.4 years were included in this cross-sectional study. Serum vitamin D, serum IL-6, and serum IL-8 levels were evaluated using an enzyme-linked immunosorbent assay. Serum vitamin D levels were categorized as deficient (<20 ng/ml), insufficient (20–30 ng/ml), and sufficient (30–100 ng/ml). The clinical severity of the disease was assessed by the fibromyalgia impact questionnaire (FIQ) and widespread pain index (WPI). Results: The mean serum IL-6 level was significantly higher in vitamin D-deficient patients in comparison with vitamin D-sufficient patients (P = 0.039). The mean serum IL-8 level was also significantly higher in vitamin D-deficient patients in comparison with vitamin D-sufficient patients (P < 0.001). A significant positive correlation was found between the serum IL-8 level and FIQ scores (r = 0.389, p = 0.001) and the WPI of the patients (0.401, p < 0.001). Serum IL-6 level was significantly correlated with the WPI of the patients (r = 0.295, p = 0.004), but not with FIQ scores (r = 0.134, p = 0.066). Serum vitamin D status was not associated with either FIQ scores or WPI. Conclusion: In FM patients, serum vitamin D deficiency is associated with higher levels of serum pro-inflammatory cytokines, and higher levels of serum pro-inflammatory cytokines are associated with greater FM impact.